1. The Field of the Invention
The present invention relates to swimming pool covers having a raised leading edge. More particularly, the present invention is directed to wheel assembly apparatus and methods for supporting the raised leading edge of a mechanically extendible swimming pool cover during pool cover extension and retraction.
2. The Prior Art
For a number of reasons, it is advantageous and increasingly common to provide swimming pools with a swimming pool cover. For example, a cover substantially reduces pool maintenance time and cost by helping to keep dirt, leaves, and other debris from getting into the pool. A swimming pool cover also decreases the need for chemical treatment, and it can further help to minimize the energy which is required to heat the pool. Additionally, the use of a swimming pool cover when the pool is not in use greatly reduces the risk that an unattended child will enter the pool and drown.
Of course, one way to cover a swimming pool is to manually extend a large cover sheet across the pool and to secure the edges of the cover sheet to the pool deck. However, such a procedure is usually quite time consuming, and, additionally, more than one individual may be required in order to cover the pool properly. Therefore, in order to increase the convenience of using a pool cover, and in order to make the frequent use of a pool cover more practicable, many swimming pool owners make use of a pool cover which is mechanically extended and retracted across the swimming pool by an electric motor.
One type of pool cover which is well adapted to such mechanical extension and retraction comprises a large, rectangular cover sheet having thickened, or beaded, side edges. The beaded edges of the cover sheet are slidably received in open channels formed in respective, parallel tracks which are positioned adjacent to opposite sides of the swimming pool. Typically, there is sufficient slack in the cover sheet such that a portion of the cover sheet rests on the surface of the water after it is fully extended across the pool, with the beaded side edges being continuously maintained in and laterally secured by the respective channels.
In order to minimize the likelihood that the pool cover's leading edge will dip into the water during extension, thereby causing water to flow onto the top of the cover sheet, mechanically extendible swimming pool covers are usually provided with a rigid leading edge. Optionally, the cover sheet may also have a central gore or a screen formed therein adjacent the leading edge of the pool cover, in order to allow for the drainage of any water which might collect on the cover sheet.
When the swimming pool cover is not in use, the cover sheet is rolled upon an elongated cylindrical member, which is located at one end of the pool. In order to cover the pool, the electric motor draws the edges of the cover sheet along the respective tracks so as to extend the cover sheet from one end of the swimming pool to the other. When the pool is to be again uncovered, the motor rolls the cover sheet back onto the cylindrical member; the cover sheet is thus retracted and stored for future use.
When a pool cover of the type described above is installed on a substantially rectangular swimming pool at the same time as such pool is being constructed, the side tracks are generally mounted inside the pool just below the pool deck. Thus, when the beaded edges of the cover sheet are properly positioned in their respective channels, the cover extends across the pool from one inside edge to the other. In such a case, the above-described pool cover may be used without modification, and it can also be mechanically extended and retracted without difficulty.
Matters are quite different, however, when a mechanically extendible pool cover is to be installed on an existing rectangular swimming pool or on any pool which has a non-rectangular shape. In such cases, it is generally preferable to install a rectangular pool cover outside of the pool such that the parallel side tracks are secured to the top of the pool deck adjacent to the pool edges. Installing the pool cover in this manner both eliminates the need to remove a portion of the pool deck and pool sides on existing pools and avoids the operational difficulties caused by attempting to mechanically extend and retract an odd-shaped swimming pool cover.
However, several difficulties arise when the pool cover is so installed outside of the pool. These difficulties are primarily due to the fact that a portion of the pool deck will necessarily underlie the pool cover after the cover is fully extended over the swimming pool, particularly in the case of odd-shaped pools. Thus, when a pool cover is installed outside of the pool, the cover will tend to drag across the pool deck's surface as it is extended and retracted, thereby making cover extension and retraction more difficult. Additionally, the rigid leading edge of the pool cover may similarly drag across the surface of the deck, thus causing undue wear both to the pool deck and to the rigid leading edge of the pool cover. Moreover, the rigid leading edge, which generally tends to sag slightly in the middle, may sometimes be unable to clear the odd-shaped or the endmost portions of the pool deck.
In order to overcome these difficulties, those skilled in the art have employed systems to raise the leading edge of the pool cover above the parallel side tracks. By raising the leading edge, one can significantly reduce the frictional forces which resist pool cover extension and retraction. Further, raising the leading edge of the pool cover eliminates the possibility that the leading edge will drag across the pool deck, thereby insuring that the leading edge will clear all portions of the deck.
However, when raising the leading edge of the pool cover, it is desirable to raise the leading edge by only the amount necessary to achieve the desired benefits. It will be appreciated, for example, that when a leading edge of the pool cover is raised by more than the necessary amount, dirt tends to get into the pool under the leading edge, thereby nullifying some of the benefits of a swimming pool cover. Additionally, if the leading edge is raised more than necessary, the pool cover's appearance is generally less desirable, and the pool cover becomes more of an obstruction.
The exact height to which the leading edge must be raised varies from pool to pool and is determined by the particular characteristics of the specific swimming pool being covered. For example, when a swimming pool is substantially rectangular, the side tracks may be secured quite close to the pool edges, which are usually at about the same height as one another. Therefore, when a pool cover of the type described above is installed on an existing rectangular pool, it is typically necessary to raise the leading edge only slightly in order to achieve the desired benefits.
This is not the case, however, when such a cover is installed on an odd-shaped pool. Since the swimming pool cover sheet is rectangular, it follows that the side tracks must necessarily be laid down in substantially parallel, straight lines, regardless of the shape of the pool. Thus, when an odd-shaped pool is to be covered, some sections of the tracks may be positioned several feet away from the pool, while other track sections would be very close to the pool edge. Since the pool deck typically slopes away from the pool in order to provide for proper drainage (this slope being generally about one downward inch for every four lateral feet), the distant sections of the tracks may be several inches lower than the portions of the pool deck which are near the edges of the swimming pool. Consequently, in order to insure proper pool cover operation on odd-shaped pools, it is sometimes necessary to raise the leading edge of the pool cover six or more inches above the two side tracks.
Since it is, therefore, nearly impossible to determine the exact height to which the leading edge of the pool cover must be raised prior to the time that the pool cover is actually being installed, it is generally preferable to use adjustable wheel assemblies to suspend the leading edge of the pool cover so that the leading edge suspension height may be varied during pool cover installation. The use of adjustable wheel assemblies thus permits the leading edge of the pool cover to be suspended at exactly the appropriate height, and it eliminates the need to separately manufacture wheel assemblies for each pool cover or to manufacture a number of different sizes of leading edge wheel assemblies.
One common type of an adjustable leading edge wheel assembly for mechanically extendible swimming pool covers is disclosed in U.S. Pat. Nos. 3,273,171 and 4,001,900. As illustrated in FIGS. 4 and 5, this prior art wheel assembly, designated generally as 58, comprises a pair of offset axles 60, each having a wheel 62 connected to one end thereof. The other ends of axles 60 are individually journaled in a bearing block 68; cotter pins 70, or other suitable means, secure axles 60 in bearing block 68 (see FIG. 5). As shown in FIG. 4, a length of substantially nonstretchable material, such as a link chain 66, serves to maintain the axles 60 in a mutually spread condition.
As illustrated, bearing block 68 is constructed so as to conform to the generally tubular inner surface of the leading edge carrier member 50. Thus, an assembled prior art wheel assembly 58 may be connected to carrier member 50 by first inserting the assembly's bearing block 68 into one open end of carrier member 50 as shown, and thereafter securing block 68 within carrier member 50 by means of a screw 64 or some other suitable securing means. The height to which the leading edge of the pool cover is raised by these prior art wheel assemblies can then be adjusted by varying the spread of the two axles 60. For example, as illustrated in FIG. 4, a hook 67 may be attached to one axle 60 and used to secure chain 66 at the appropriate place so as to maintain the desired axle spread.
Although the adjustable wheel assemblies of the prior art described above have proven generally adequate to raise a leading edge of the pool cover to the desired height, there are several problems associated with their use. First, these wheel assemblies are somewhat difficult and time consuming to manufacture. Each of the axle rods must be precisely bent to the proper offset shape. Such bending of the axle rods is difficult and may often not be done with enough precision to insure that the wheels will be properly aligned. Holes must also be drilled in one end of the axle rods to receive the cotter pins; and a chain, a hook, and wheels must be separately attached to the completed axles.
Equally important, it is quite time consuming to assemble and install the prior art wheel assemblies. Prior to assembly, a bearing block must first be drilled to receive the two axles. The offset axles are then inserted into the bearing blocks, with cotter pins being thereafter inserted through the holes in the axle rods. The completed wheel assembly's bearing block must then be placed into one end of the leading edge of the pool cover carrier member and secured therein by means of a screw. Significantly, this latter step typically requires drilling through the leading edge carrier member at the installation site.
Moreover, the prior art wheel assemblies also have a number of operational difficulties. For example, in order to make the wheel assemblies adjustable, an oversized chain is typically used. Consequently, when the wheel assembly is raised to near its maximum height, the chain tends to drag across the surface of the pool deck, thereby causing increased noise, wear on the pool deck, and possible interference with the rotation of the wheels. Although the excess chain may be removed, this would render it impossible to further adjust the height of the leading edge, if such adjustment should ever be needed. Additionally, since it is difficult to precisely bend the axle rods, the two wheels are often not properly aligned with one another. Thus, the wheels may tend to drag or slide across the pool deck as the pool cover is extended and retracted.
Accordingly, it would be an improvement in the art to provide a swimming pool cover leading edge wheel assembly which can be manufactured, assembled, and installed with a minimum number of steps and component parts. It would also be an improvement in the art to provide a leading edge wheel assembly which does not require the precision bending of axle rods and does not require the drilling of axle rods. Additionally, it would be an improvement in the art to provide an adjustable leading edge wheel assembly which operates smoothly, dependably, and without interference from a dragging chain or other component parts. It would be a still further improvement in the art to provide a method for suspending the leading edge of a swimming pool cover which obviates the need for a complex manufacturing process but which provides a means for adjusting the height of the leading edge, without sacrificing smooth and dependable pool cover operation. Such apparatus and methods are disclosed and claimed herein.